Solution (a)
(i) Gabriel Phthalimide Synthesis: [1 Mark]
Used for the preparation of primary aliphatic amines. Phthalimide is treated with ethanolic $\text{KOH}$ to form potassium phthalimide, which is then heated with an alkyl halide followed by alkaline hydrolysis.
$$ \text{C}_6\text{H}_4(\text{CO})_2\text{NH} \xrightarrow{\text{KOH(alc)}} \text{C}_6\text{H}_4(\text{CO})_2\text{NK} \xrightarrow{\text{R-X}} \text{C}_6\text{H}_4(\text{CO})_2\text{NR} \xrightarrow{\text{NaOH(aq)}} \text{C}_6\text{H}_4(\text{COOK})_2 + \text{RNH}_2 $$Example: $\text{R} = \text{C}_2\text{H}_5$ (Ethylamine).
(ii) Carbylamine Reaction: [1 Mark]
Aliphatic or aromatic primary amines when heated with chloroform and ethanolic $\text{KOH}$ form isocyanides (carbylamines), which have a foul smell.
$$ \text{R-NH}_2 + \text{CHCl}_3 + 3\text{KOH(alc)} \xrightarrow{\Delta} \text{R-NC} + 3\text{KCl} + 3\text{H}_2\text{O} $$Example: $\text{CH}_3\text{NH}_2 + \text{CHCl}_3 + 3\text{KOH} \rightarrow \text{CH}_3\text{NC} + 3\text{KCl} + 3\text{H}_2\text{O}$
(iii) Hoffmann Bromamide Degradation Reaction: [1 Mark]
Primary amides react with bromine in an aqueous or ethanolic solution of $\text{NaOH}$ to form primary amines with one carbon atom less than the original amide.
$$ \text{R-CONH}_2 + \text{Br}_2 + 4\text{NaOH} \rightarrow \text{R-NH}_2 + \text{Na}_2\text{CO}_3 + 2\text{NaBr} + 2\text{H}_2\text{O} $$Example: $\text{CH}_3\text{CONH}_2 + \text{Br}_2 + 4\text{NaOH} \rightarrow \text{CH}_3\text{NH}_2 + \text{Na}_2\text{CO}_3 + 2\text{NaBr} + 2\text{H}_2\text{O}$
Solution (b)
(i) Sequence Analysis: [1.5 Marks]
- Step 1: $\text{CH}_3\text{CH}_2\text{Cl} \xrightarrow{\text{KCN}} \text{CH}_3\text{CH}_2\text{CN} (\text{A})$
- Step 2: $\text{CH}_3\text{CH}_2\text{CN} \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2 (\text{B})$
- Step 3: $\text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2 \xrightarrow{\text{HNO}_2} \text{CH}_3\text{CH}_2\text{CH}_2\text{OH} (\text{C